Process for the preparation of solid iron (III) complexes

ABSTRACT

Fe(III) complexes having high bulk density and a process for the production of the same without the generation of heavy metal-contaminated effluents are disclosed. Solid complexes of EDTANaFe and EDTAKFe having high bulk densities are formed by reaction with ferric sulfate containing low chromium levels, followed by total drying of the resulting mixture in the same processing equipment without the prior separation of the sulfate salts formed.

This is a division of application Ser. No. 07/700,722, filed May 15,1991, now U.S. Pat. No. 5,159,094.

BACKGROUND OF THE INVENTION

Conventional processes for the production of solid Fe(III) chelates foragricultural and other uses generate waste crystal liquors with highconcentrations of iron and heavy metals, particularly chromium. Suchheavy metals are problematic from an environmental standpoint. Theeconomic implications of properly disposing of such streams aresignificant, and are often prohibitive. In addition, the waste liquorcan contain some soluble Product. Although disposal of the waste liquorswithout recovering the product results in yield loss, recovery ofcontained product is not economical.

A conventional process for producing the complexes involves reactingchelating agents, such as EDTANa₄ or DTPANa₅, with ferric chloridesolution, followed by filtration, washing and drying. However, one majorsource of chromium contamination is the ferric chloride used as theferric iron source. Where low cost grade ferric chloride derived fromscrap iron is used, the chromium concentration of the waste streamsproduced is on the order of 30 ppm. Higher grade ferric chloride can beused, which can reduce the chromium concentration in the waste streamsto about 2-3 ppm; however, this higher grade ferric chloride is moreexpensive. A further drawback of ferric chloride is the highly corrosiveproperties of the slurries and liquors produced from the chelatingagent/ferric chloride reactions.

Prior art drying processes include spray drying and drum drying.However, the resulting product is often very dusty, which createshandling problems jacketed vessel. Scrapers on the agitator shaft areinstrumental in freeing the heat transfer surface of dried material. Theequipment produces some agglomeration, which leads to the high bulkdensity of the product. In addition, high shear choppers reduce largeagglomerate masses to promote thoroughly dried particle interiors.Preferably the equipment utilizes hydraulic drive. Such equipment isavailable from Littleford Bros., Inc., Florence, Ky.

Prior to drying, a slurry is formed by reaction of pH-adjusted chelatingagents with an iron source, preferably 50% ferric sulfate solution. Thereaction is illustrated for EDTANa₄ as follows: ##STR1## Other salts ofthe chelating agents can be used, such as the potassium salts. ThePH-adjusted chelating agent is prepared by neutralizing free alkalimetal (e.g., sodium or potassium) hydroxide with the acid chelate, orwith a mineral acid, such as 50% or 93% sulfuric acid. The chelatingagent is available from W. R. Grace & Co.-Conn. as Hamp-Ene^(R) 100S andis one of the feedstocks to the reactor/dryer. A slurry is then formedby reacting the chelating agent with ferric sulfate solution at about40°-50° C. Preferably the chelating agent is as concentrated as possiblein order to reduce the evaporative load on the drying equipmentutilized. In the same piece of equipment, the resulting slurry is vacuumdried to a blend of the alkali metal salt of the iron (III) chelate andalkali metal sulfate. In contrast to conventional spray dryingprocesses, the instant vacuum drying employs relatively long residencetimes which depend upon the steam pressure and the vacuum applied.

Since the entire product is vacuum dried without separation of thealkali metal sulfate salt formed, no effluent is produced and the yieldis 100% (less any physical losses that occur). Although the iron contentof the final product is lower than the prior art products from which thesalt has been separated, a significant savings results from the absenceof any effluent and the said 100% yield of product.

One surprising aspect of the instant process is the high bulk density ofthe resulting product formed. A comparison of the total iron content andbulk densitites of the products formed in accordance with the instantinvention with that of the iron chelate formed from a prior art process(wherein the alkali metal chloride salt has been separated) isillustrated in Table 1.

                  TABLE 1                                                         ______________________________________                                                                 BULK DENSITY                                         PRODUCT          % Fe    LB/Cu Ft                                             ______________________________________                                        EDTANaFe (prior art)                                                                           12.6    37.1                                                 EDTANFe/Na.sub.2 SO.sub.4                                                                      8.73    62.1                                                 EDTAKFe/K.sub.2 SO.sub.4                                                                       7.80    61.8                                                 ______________________________________                                    

The very high bulk densities of the instant products is a furtheradvantage which offsets the slightly lower iron content of the productsdue to the presence of the alkali metal sulfate.

The total dried product may be milled to remove any gritty material. Forcommercial applications, it may be desirable to have 100% of thematerial pass through a 25 mesh sieve. A sieve analysis has demonstratedthat about 7% of EDTANaFe/Na₄ SO₄ is greater than 25 mesh and thereforerequires milling to meet the desirable specifications.

It would be obvious to those silled in the art that the disclosedprocess should be generally applicable to preparation of the Fe(III)complexes of ligands other than EDTA.

The following examples will serve to illustrate various embodiments ofthe instant invention.

EXAMPLE 1 Production of DETANaFe/Na₂ SO₄

The equipment used was a Littleford reactor/dryer MR5. EDTANa₄ solutionwas charged to a hold tank and free alkali therein was neutralized with93% sulfuric acid. As the iron source, 50% Fe₂ (SO₄)₃ was used. The Fe₂(SO₄)₃ was charged to the reactor/dryer and warmed to about 40° C. Theneutralized chelate was then added in an amount of 3% excess over iron,and the resulting slurry was vacuumed dried to a blend of EDTANaFe andNa₂ SO₄. The data are provided in Table II.

EXAMPLE 2 Production of EDTAKFe/K₂ SO₄

The reaction and drying were carried out as in Example 1, except thatthe chelating agent was EDTAK₄ solution. The data are provided in TableIII.

                                      TABLE II                                    __________________________________________________________________________    SCALE = 1.0 LB MOLE OF IRON                                                                   % Active                                                                            Molecular Weight At                                                     Ingredient                                                                          Weight                                                                              Moles                                                                             100%                                                                              Actual A.I.                                                                         Sp. Gravity                                                                         Lb/gal                                                                            Gallons                   __________________________________________________________________________    TO PRODUCE EDTANaFe - PRODUCT CODE NOS. 150 & 600                             HampEne 100 S (EDTANa4)                                                                       38.0% 380.2 1.030                                                                             392 1031  1.270 10.6                                                                               97.4                     Free NaOH in H-100 S                                                                          1.5%  40.0  0.386                                                                              15                                           H2SO4           93.0% 98.0  0.193                                                                              19  20   1.840 15.3                                                                               1.3                      Fe2(SO4)3       50.0% 399.9 0.500                                                                             200  400  1.440 12.0                                                                               33.3                     Water                                 0                                       Total                               1451            132.1                     PRODUCT                                                                       EDTANaFe              367.1 1.000                                                                             367                                           Na2SO4                142.0 1.693                                                                             240                                           Total Anhydrous Pure Product    608                                           Total Product @ Fe Content of                                                                 8.7%            642                                           __________________________________________________________________________     Note: the 8.7% Fe value was the Fe content of product produced from the       Littleford trial                                                         

                                      TABLE III                                   __________________________________________________________________________    TO PRODUCE EDTAKFe                                                            HampEne K4 100 S (EDTAK4)                                                                     44.4% 444.6 1.030                                                                             458 1031  1.320 11.0                                                                              93.8                      Free KOH in H-K4-100 S                                                                        1.5%  56.1  0.276                                                                              15                                           H2SO4           93.0% 98.0  0.138                                                                              14  15   1.840 15.3                                                                              0.9                       Fe2(SO4)3       50.0% 399.9 0.500                                                                             200  400  1.440 12.0                                                                              33.3                      Water                                 0                                       Total                               1446            128.1                     PRODUCT                                                                       EDTAKFe               383.2 1.000                                                                             383                                           K2SO4                 174.3 1.638                                                                             285                                           Total Anhydrous Pure Product    669                                           Total Product @ Fe Content of                                                                 7.8%            716                                           __________________________________________________________________________     Note: the 7.8% Fe value was the Fe content of product produced from the       Littleford trial                                                         

What is claimed is:
 1. A dry solid composition consisting essentially ofEDTANaFe.xH₂ O and Na₂ SO₄ having a bulk density of about 60 pounds percubic foot.
 2. A dry solid composition consisting essentially ofEDTAKFe.xH₂ O and K₂ SO₄ having a bulk density of about 60 pounds percubic foot.
 3. Iron (III) complexes of alkali metal salts of EDTA,produced by a process comprising:a. Neutralizing free alkali present inan alkali metal salt solution of EDTA with acid; b. Reacting theneutralized alkali metal salt solution with ferric sulfate to form aslurry containing alkali metal sulfate; c. Vacuum drying said slurrywithout the prior separation of said alkali metal sulfate, said reactingand vacuum drying steps being carried out in the same processingequipment.